Theory now gives the pedestrian 5...c6.
Yet it may seem unjust for Black to be relegated to
this move, given that his development has been no less
rapid than White's. Indeed, Black has available a
dynamic alternative.

5...Nc6

After the continuation 6. Qxd5 Nb4,

White has three retreats that keep the c2 square protected:

A. 7. Qb3
B. 7. Qc4
C. 7. Qe4

A. 7. Qb3

7...Qh4

The threat is now 8...Qe4+, not only to regain the pawn
but also to force the White king to protect the c2 square.
Various tries by White to keep the extra pawn:

A1. 8. Nf3
A2. 8. d3
A3. 8. c3

A1. 8. Nf3

8...Qe4+ 9. Kd1 Qg6

Inhibiting the development of the f1-bishop, while
sidestepping White's threat of 10. Qxf7+ Kxf7 11. Ng5+.
The displacement of White's king gives Black
compensation for the pawn.

The threat was 10...Bxh3 followed by taking on f2.
After 10. Bg5 Qh5, the capture of White's knight
threatens to unhinge White's game at g5 and f3.

10...Qd4 11. Be3 Qxe5

Black seems to have no problems.

A3. 8. c3

8...Qe4+ 9. Kd1 Nd3 10. Nh3

10. Bxd3 loses to 10...Qxg2.

10...Nxe5

10...Qe1+ 11. Kc2 Nxe5 12. d4 Nc6 13. Bg5 gains
valuable time, as 13...Qxa1 loses to 14. Bc4
threatening mate and the queen. Black could vary
by 12...Qe4+ (intending to transpose to the
text line after 13. Ke1), but the text move is
more straightforward.

11. d4 Nc6 12. Bc4 Qxg2 13. Bxf7+ Kd8 14. Re1 Be7
15. Nf4 Qg4+

A really mixed up position in which Black seems not to
be at a disadvantage.

B. 7. Qc4

7...d5

White now has no appealing choices:

B1. 8. exd6 Bxd6 gives Black a significant lead in
development. The attempt to force the closure of the
e-file by 9. Qe4+ Be6 10. Bc4 O-O 11. Bxe6 (hoping for
11...fxe6) fails to 11...Re8 and ...Rxe6.